This invention relates to the preparation of miniaturized sensors which use fluids, and the arrangement of a measuring system using the sensors. The described arrangement is especially useful for creating liquid drops or gas bubbles and meniscus effects thereof, as part of a sensor arrangement.
One of the best representatives of liquid electrodes used as sensors, is the mercury drop electrode. The introduction of the laboratory static mercury drop electrode or SMDE, several years ago, represents one of the essential contributions to modern polarographic and voltammetric techniques and instrumentation. This type of electrode incorporates in some respects the properties of the dropping mercury electrode (DME) used by J. Heyrovsky at the beginning of polarography and the hanging mercury drop electrode or HMDE used mainly in voltammetric stripping analysis. See, W. M. Peterson, Amer. Lab. 1/2, Vol. 51, 1296 A (1979); L. Novotny, PhD Thesis, J. Heyrovsky Institute, Prague (1980); Czech. Pat. A.O. 202 316, Prague, (1978-1989); Samec, et al., J. Electroanal. Chem., 100/841, (1979); A. W. Adamson, Physical Chemistry of Surfaces, J. Willey Inc. (1972); and J. Koryta, et al. J. Electroanal. Chem., 75/211 (1977).
Commercially produced SMDE systems represent a standard type of device used in chemical laboratories. However, this type of instrument does not meet present requirements, or meets them only to a very limited extent. It does not enable, for example:
the generation of drops of various sizes, e.g. of volumes between 0.0005 .mu.l to 1 .mu.l;
a choice or change in parameters for different modes in a very broad range such as drop-time between 0.1 and 200-300 seconds for a DME, or time of drop growth for an HMDE between 20 milliseconds and 20 seconds;
drop size reproducibility for an HMDE down to .+-.0.1-0.2% and reproducibility of a DME, at constant potential, down to .+-.0.001%;
a very good mechanical stability of the drop in HMDE, etc., even under considerable mechanical or ultrasonic vibrations at very negative potentials, upon sudden changes of potentials, at very high concentrations of surface active substances, etc.
working in organic solvents, even at extremely negative potentials, e.g. -2.5 V to -3.1 V (using saturated LiCl in CH.sub.3 OH);
reasonable reproducibility, e.g., .+-.1 to .+-.3% and better mini-, semimicro- and microelectrodes, in DM.mu.E, HMD.mu.E, SMD.mu.E modes, as well as meniscus mercury microelectrodes (DM.mu.E refers to dropping mercury microelectrodes, HMD.mu.E to hanging mercury drop microelectrodes and SMD.mu.E to static mercury drop microelectrodes);
a stepwise growing of Hg drop mini- and microelectrodes, e.g., the stepwise growing of an HMDE or HMD.mu.E, the number of steps representing one of the electrode parameters;
applicability in all mentioned modes independently of any analyzer or in combination with external analyzers, microcomputers, etc.;
the applicability of the sensor in vertical as well as in nearly horizontal positions, depending partly on the mode used; or
the design of a miniaturized portable system, relatively simple to handle, including special "pen-type" electrodes.
Thus, while some versions of electrodes which are based on a liquid/liquid interface have been used, they cannot perform or do not have the foregoing characteristics which would be useful.